Flattening Method and Flattening Apparatus

ABSTRACT

A flattening method can flatly process a surface of a metal film as an interconnect material over the entire film surface at a sufficiently high processing rate even when the metal film has initial surface irregularities. The flattening method for processing and flattening a surface of a metal film formed on a workpiece and having initial surface irregularities, including: coating only recessed portions of the initial surface irregularities of the metal film with a solid or pasty coating material; and processing the surface of the metal film by electrolytic processing using no abrasive.

TECHNICAL FIELD

The present invention relates to a flattening method and a flatteningapparatus, more particular to a flattening method and a flatteningapparatus useful for processing and flattening a surface of aninterconnect material (conductive film) of a metal film, such as copperfilm, which has been formed on a surface of a substrate, such as asemiconductor wafer, and embedded into fine interconnects recessesformed in the surface of the substrate.

BACKGROUND ART

In recent years, instead of using aluminum or aluminum alloys as aninterconnect material for forming circuits on a substrate such as asemiconductor wafer, there is an eminent movement towards using copperwhich has a low electric resistivity and high electromigrationresistance. Copper interconnects are generally formed by filling copperinto fine interconnects recesses formed in a surface of a substrate.There are known various techniques for forming such copperinterconnects, including chemical vapor deposition (CVD), sputtering,and plating. According to any such technique, a copper film is formed inthe substantially entire surface of a substrate, followed by removal ofunnecessary copper by polishing.

FIGS. 1A through 1C illustrate, in a sequence of process steps, anexample of forming such a substrate W having copper interconnects. Asshown in FIG. 1A, an insulating film 2, such as an oxide film of SiO₂ ora film of low-k material, is deposited on a conductive layer 1 a inwhich semiconductor devices are formed, which is formed on asemiconductor base 1. Contact holes 3 and trenches 4 as interconnectsrecesses are formed in the insulating film 2 by the lithography/etchingtechnique. Thereafter, a barrier layer 5 of TaN or the like is formed onthe surface, and a seed layer 7 as an electric supply layer forelectroplating is formed on the barrier layer 5 by sputtering, or CVD,or the like.

Then, as shown in FIG. 1B, copper plating is performed onto the surfaceof the substrate W to fill the contact holes 3 and the trenches 4 withcopper and, at the same time, deposit a copper film 6 on the insulatingfilm 2. Thereafter, the copper film 6, the seed layer 7 and the barrierlayer 5 on the insulating film 2 are removed by chemical mechanicalpolishing (CMP) or the like so as to make the surface of the copper film6 filled in the contact holes 3 and the trenches 4 and the surface ofthe insulating film 2 lie substantially on the same plane. Interconnectscomposed of the copper film 6, as shown in FIG. 1C, are thus formed inthe insulating film 2.

Components in various types of equipments have recently become finer andhave required higher accuracy. As sub-micron manufacturing technology isbecoming common, the properties of materials are more and moreinfluenced by the processing method. Under these circumstances, with aconventional mechanical processing method in which a processing objectin a workpiece is physically destroyed and removed from the workpiece bya tool, many defects may be produced, deteriorating the properties ofthe workpiece. Thus, it is increasingly important to perform processingwithout deteriorating the properties of the materials.

Some processing methods, such as chemical polishing, electrolyticprocessing, and electrolytic polishing, have been developed in order tosolve this problem. In contrast with the conventional physicalprocessing, these methods perform removal processing or the like throughchemical dissolution reaction. Therefore, these methods do not sufferfrom defects, such as formation of a damaged layer and dislocation, dueto plastic deformation, so that processing can be performed withoutdeteriorating the properties of the materials.

Chemical mechanical polishing (CMP), for example, generally necessitatesa complicated operation and control, and needs a considerably longprocessing time. In addition, a sufficient cleaning of a substrate mustbe conducted after the polishing treatment. This also imposes aconsiderable load on the slurry or cleaning liquid waste disposal.Accordingly, there is a strong demand for omitting CMP entirely orreducing a load upon CMP.

In order to solve such problems, an electrolytic processing method hasbeen proposed which involves providing an ion exchanger as a processingmember between an electrode and a workpiece, and using a liquid having ahigh electric resistance, such as pure water or ultrapure water, as anelectrolytic liquid in carrying out processing of the workpiece, therebyreducing the mechanical stress on the workpiece and simplifyingpost-cleaning (see, for example, Japanese Patent Laid-Open PublicationNo. 2003-145354).

DISCLOSURE OF INVENTION

As shown in FIG. 2A, in a substrate having a surface copper film as aninterconnect material for the formation of copper interconnects, forexample, there generally exist a pattern region P consisting of a largenumber of trenches 4 provided at a predetermined pitch in an insulatingfilm 2, and a copper film (metal film) 6 embedded in the trenches 4 anddeposited over the trenches 4 and the insulating film 2, and a fieldregion F surrounding the pattern region P and consisting of theinsulating film 2 and the copper film 6 deposited thereon. The patternregion P has initial surface irregularities which vary depending on thedensity, width, etc. of interconnects to be formed.

When processing and flattening the surface of the copper film 6 byelectrolytic processing, the initial surface irregularities of thecopper film 6 produce a difference in the intensity of electric fieldbetween an electrode and the copper film 6. In particular, the intensityof electric field is higher in the pattern region P in which raisedportions are concentrated, whereby the amount of reaction species ions,i.e. ionic substances for promoting the dissolution of a conductive filmto be polished, e.g. hydroxide ions in the case of a copper conductivefilm, supplied is larger in the pattern region P than that in the fieldregion F. This results in a higher processing rate of the copper film 6in the pattern region P than that in the field region F. Further, thereis no significant difference in the processing rate of copper film 6between recessed portions 6 a and raised portions 6 b, together formingthe irregularities, that is, the recessed portions 6 a and the raisedportions 6 b are processed almost at the same rate. Accordingly, theinitial surface irregularities will remain unremoved during processing,as shown in FIGS. 2B and 2C, and it is difficult to flatten the copperfilm 6 over the entire surface. If electrolytic processing is furthercontinued, the copper embedded in the trenches 4 will be processed andremoved, as shown in FIG. 2D, resulting in a decrease in the volume ofinterconnects and thus a rise in the resistance of interconnects.

An electrolytic processing method has therefore been employed which usesan electrolytic liquid containing a surface film-forming agent, such asan oxidizing agent or a complexing agent, in carrying out processing ofsuch a processing object as the copper film 6. This method can suppressan electrolytic dissolution reaction within the recessed portions 6 a ofthe copper film 6 so as to make the processing rate of the recessedportions 6 a slower than that of the raised portions 6 b, and thusselectively process the raised portions 6 b, thereby increasing theflatness of the processed surface. According to this method, however,when a high voltage is applied in order to obtain a high processingrate, the effect of suppressing the electrolytic reaction through theformation of a surface film is insufficient for producing an adequatesurface irregularities-removing effect.

Further, since the polishing (processing) rate of the copper film 6 inthe pattern region P is higher than the polishing rate of the copperfilm 6 in the field region F, as described above, a concave 9 can beformed in the entire copper film 6 lying in the pattern region P, asshown in FIGS. 3A through 3C. The size of the concave 9 can beconsiderably large depending on the configuration, etc. of the patternregion P, which makes it difficult to flatten the entire surface of thecopper film 6.

A demand, therefore, exits for a technique that can equalize thepolishing rate of copper film 6 in the pattern region P with thepolishing rate of copper film 6 in the filed region F, as shown in FIGS.4A and 4B, thus flatly polishing the entire surface of copper film 6despite the presence of the pattern region P and the field region F, asshown in FIG. 4C. Various attempts made thus far, however, have provendifficulty in developing such a technique for equalizing the polishingrate of copper film 6 in the pattern region P with the polishing rate ofcopper film 6 in the field region F.

The present invention has been made in view of the above situation inthe background art. It is therefore an object of the present inventionto provide a flattening method and apparatus which can flatly process asurface of a metal film (conductive film), e.g. a copper film as aninterconnect material, over the entire film surface at a sufficientlyhigh, processing rate even when the metal film has initial surfaceirregularities.

In order to achieve the above object, the present invention provides aflattening method for processing and flattening a surface of a metalfilm formed on a workpiece and having initial surface irregularities,comprising: coating only recessed portions of the initial surfaceirregularities of the metal film with a solid or pasty coating material;and processing the surface of the metal film by electrolytic processingusing no abrasive.

According to this flattening method, processing of recessed portions ina surface of a metal film can be suppressed by the coating of therecessed portions with a coating material so that raised portions of themetal film can be selectively processed by electrolytic processing,whereby the surface of the metal film can be flattened. Further, asufficiently high processing rate can be obtained by using, as thecoating material, a solid or pasty material which is highly adhesive tothe metal film and does not separate from the metal film even whencarrying out electrolytic processing at an applied voltage of e.g. notless than 10 V.

Though a common electrolytic solution may be employed in carrying outelectrolytic processing, it is desirable to use ultrapure water, purewater or a liquid having an electric conductivity of not more than 500μS/cm. This can materially reduce contamination of the surface ofworkpiece and can facilitate treatment of the waste liquid afterprocessing.

In a preferred embodiment of the present invention, the flatteningmethod further comprises removing the coating material which has notbeen processed by the electrolytic processing and remains on the surfaceof the metal film, and further processing the surface of the metal film.

When coating recessed portions in the surface of a metal film with acoating material, and processing the surface of the metal film byelectrolytic processing while suppressing processing of the metal filmat the recessed portions, the coating material, which may be aninsulating material, can remain unremoved on the surface of the metalfilm. In such a case, the coating material may be removed, for examplewhen raised portions have been removed and the coating material hasbecome exposed, and the surface of the metal film may be subjected tofurther processing, whereby a flattened metal surface free of thecoating material can be obtained. The processing of the metal filmsurface after the removal of the coating material can be carried out byelectrolytic processing using, for example, an electrolytic solution orultrapure water, or by any other conventional processing method, such asCMP.

The coating material may be an insulating material having a resistivityof not less than 10⁶ Ω·cm or a conductive material having a resistivityof not more than 103 Ω·cm.

The use, as the coating material, of an insulating material having aresistivity of not less than 10⁶ Ω·cm (conductivity of not more than 1μS/cm) substantially inhibits passage of an electric current through thecoating material. This can inhibit electrolytic reaction at thoserecessed portions of the metal film which are coated with the coatingmaterial, thereby preferentially removing raised portions of the metalfilm. Examples of the insulating material include a photoresist, apaint, an oil-based ink and a quick-drying adhesive.

The use, as the coating material, of a conductive material having aresistivity of not more than 10³ Ω·cm (electric conductivity of not lessthan 1 μS/cm) allows an electric current to pass through the coatingmaterial, thereby allowing electrolytic reaction to progress also at thesurface of the conductive material. This allows passage of an electroncurrent through the coating material to the recessed portions of themetal film, which makes it possible to uniformize the current densityover the entire surface of the metal film and to thereby uniformlyprocess the metal film except the coated portions. Examples of theconductive material include a conductive paint, a conductive ink, aconductive adhesive and a conductive paste. These conductive materialscan be prepared by mixing a resin with conductive particles, such asfine metal particles or carbon particles, and the conductivity can beadjusted by the mixing ratio of the conductive particles.

It is preferred that the coating material, which is either an insulatingmaterial or a conductive material, have a certain degree ofprocessability and be processed at a slower rate than the metal film byelectrolytic processing.

In a preferred embodiment of the present invention, only the recessedportions of the initial surface irregularities of the metal film arecoated with the coating material by applying the coating material ontothe entire surface of the metal film, and then removing only the coatingmaterial lying on the raised portions of the initial surfaceirregularities.

Only the recessed portions of the initial surface irregularities of ametal film can be coated with the coating material, for example, byapplying an oil-based ink, an oil paint or the like, onto the entiresurface of the metal film, and then wiping off the oil-based ink, theoil paint or the like on the metal film with an alcohol or a thinner, orby applying a resist onto the entire surface of a metal film, followedby exposure and development of the resist.

In a preferred embodiment of the present invention, only the recessedportions of the initial surface irregularities of the metal film arecoated with the coating material by selectively applying the coatingmaterial onto the recessed portions of the metal film.

Only the recessed portions of the initial surface irregularities of ametal film can be coated with the coating material, for example, byselectively applying an ink only onto the recessed portions of the metalfilm by an ink jet method.

In a preferred embodiment of the present invention, the processing ofthe surface of the metal film by the electrolytic processing is carriedout by applying a voltage between a processing electrode, disposed closeto the metal film of the workpiece, and a feeding electrode for feedingelectricity to the metal film, supplying a liquid into the space betweenthe workpiece and at least one of the processing electrode and thefeeding electrode, in which space a processing member is present, andmoving the workpiece relative to at least one of the processingelectrode and the feeding electrode.

Though a common electrolytic solution may be used as the liquid, it isdesirable to use ultrapure water, pure water or a liquid having anelectric conductivity of not more than 500 μS/cm. This can materiallyreduce contamination of the surface of a workpiece and can facilitatetreatment of the waste liquid after processing.

The processing member is preferably composed of an ion exchanger or amaterial containing an ion exchanger.

The use of an ion exchanger or a material containing an ion exchangerfor the processing member can process and flatten a surface of a metalfilm while promoting dissociation of water molecules in a liquid, suchas ultrapure water, into hydroxide ions and hydrogen ions. It is alsopossible to use a CMP pad, a fixed-abrasive pad, a PVA sponge, etc. asthe processing member.

In a preferred embodiment of the present invention, the processing ofthe surface of the metal film by the electrolytic processing is carriedout by applying a voltage between a processing electrode, disposed closeto the metal film of the workpiece, and a feeding electrode for feedingelectricity to the metal film, supplying a liquid between the workpieceand at least one of the processing electrode and the feeding electrode,and moving the workpiece relative to at least one of the processingelectrode and the feeding electrode.

In a preferred embodiment of the present invention, the processing ofthe surface of the metal film by the electrolytic processing is carriedout by bringing a contact member, disposed beside the processingelectrode and/or the feeding electrode, into contact with the metal filmsurface.

By thus electrolytically processing the surface of the metal film bybringing a contact member into contact with the metal film surface, thesolid or pasty coating material can be processed (removed) whileadjusting the processing rate. A CMP pad, a fixed-abrasive pad, a PVAsponge, etc. can be used as the contact member. An ion exchanger or amaterial containing an ion exchanger may also be used.

The present invention also provides a flattening apparatus comprising: acoating material processing apparatus for coating only recessed portionsof initial surface irregularities of a metal film with a solid or pastycoating material; and an electrolytic processing apparatus forprocessing the surface of the metal film by electrolytic processingusing no abrasive.

The coating material processing apparatus is, for example, a resistprocessing apparatus.

The present invention also provides another flattening method forpolishing and flattening a surface of a metal film (conductive film)formed on a workpiece and having a pattern region and a field region,comprising: carrying out a first polishing of the metal film surface insuch a manner that the polishing rate of the metal film in the patternregion is higher than the polishing rate of the metal film in the fieldregion; and carrying out a second polishing of the metal film surface insuch a manner that the polishing rate of the metal film in the fieldregion is higher than the polishing rate of the metal film in thepattern region.

According to this flattening method, the surface of the metal film(conductive film) can be polished flatly over the entire surface of theworkpiece by mainly removing the initial surface irregularities of themetal film in the pattern region by the first polishing, and then mainlyremoving the surface level difference in the metal film between thepattern region and the field region by the second polishing. Mostpreferably, the polishing rate of the metal film of the field region inthe first polishing and the polishing rate of the metal film of thepattern region in the second polishing are both zero.

The first polishing is to be continued until the initial surfaceirregularities of the metal film in the pattern region is removed. Whenthe polishing rate for the metal film of the pattern region in the firstpolishing is small, the thickness of the metal film, to be subjected tothe second polishing to remove the surface level difference in the metalfilm between the pattern region and the field region, becomesundesirably small. It is, therefore, desirable to make the polishingrate in the first polishing of the metal film of the pattern region atleast twice the polishing rate of the metal film of the field region soas to produce a larger surface level difference in the metal filmbetween the pattern region and the field region.

Preferably, at least one of the first polishing and the second polishingis carried out by electrolytic processing.

This can eliminate a CMP processing or reduce the burden on CMP.

In a preferred embodiment of the present invention, the first polishingand the second polishing are carried out by applying a voltage between aprocessing electrode, disposed close to the surface of the metal film ofthe workpiece, and a feeding electrode for feeding electricity to themetal film, supplying a liquid into the space between the workpiece andat least one of the processing electrode and the feeding electrode, inwhich space a processing member is present, and moving the workpiecerelative to at least one of the processing electrode and the feedingelectrode.

By thus carrying out the polishing of the metal film throughelectrochemical interaction at a lower pressure than conventional CMP,deterioration of the properties of the metal film can be prevented.Ultrapure water, pure water, or a liquid having an electric conductivityof not more than 500 μS/cm or an electrolytic solution is preferablyused as the liquid. This can materially reduce contamination of thesurface of the workpiece, and can facilitate treatment of the wasteliquid and cleaning after processing.

Preferably, the processing member is composed of an ion exchanger or amaterial containing an ion exchanger.

In a preferred embodiment of the present invention, the first polishingis carried out while keeping the processing member in contact with thepattern region, and the second polishing is carried out while keepingthe processing member contactless with the pattern region.

Especially when an ion exchanger or the like is used as the processingmember, the second polishing can be carried out at a lower polishingrate of the metal film in the pattern region than the first polishing bycarrying out the first polishing while keeping the processing member(ion exchanger or the like) in contact with the pattern region andcarrying out the second polishing while keeping the processing membercontactless with the pattern region. The processing member may be incontact with the field region of the metal film during the secondpolishing.

In order to carry out polishing while keeping the processing membercontactless with the pattern region, it is necessary to make deformationof the processing member due to contact pressure small. For thispurpose, a processing member having high rigidity, for example, onehaving high Young's modulus or one having an increased thickness toincrease the moment of inertia of area, may be used. It is also possibleto reduce the contact pressure between the processing member and themetal film of the field region.

In a preferred embodiment of the present invention, the first polishingis carried out while keeping the processing member in contact with thepattern region, and a resistance-forming processing of the patternregion is carried out prior to or simultaneously with the secondpolishing.

By carrying out a resistance-forming processing to form a resistance inthe pattern region, the polishing rate of the metal film in the patternregion can be decreased. The following are examples of theresistance-forming processing:

(1) Processing of exposing the pattern region to an oxidizing agent(H₂O₂, O₃, etc.) or a complexing agent so as to passivate or complex themetal film surface in the pattern region, thereby retarding reactionspecies ions reaching the metal film surface in the pattern region;

(2) Processing of introducing an additive, having insulating properties,into a processing liquid so as to coat the metal film surface in thepattern region with the additive (insulating material), therebypreventing reaction species ions from reaching the metal film surface inthe pattern region; and

(3) Processing of introducing an additive, for example, a corrosioninhibitor such as BTA (benzotriazole), which inhibits reaction betweenreaction species ions and the metal film, into a processing liquid,thereby inhibiting the reaction itself between the reaction species ionsand the metal film.

Though the resistance-forming processing is desirably effected only inthe pattern region, the processing may be effected also in the fieldregion, provided that the resistance formed can be removed from thefield region by the contact pressure of the processing member or acontact member. The resistance-forming processing may be carried outeither prior to or simultaneously with the second polishing.

In a preferred embodiment of the present invention, the second polishingis carried out while keeping the processing member contactless with thepattern region and simultaneously carrying out the resistance-formingprocessing of the pattern region.

By keeping the processing member contactless with the pattern regionduring the second polishing, a resistance, such as a passive film, acomplex, or an insulating material, which has been formed by theresistance-forming processing on the surface of the metal film of thepattern region, can be prevented from being removed by its contact withthe processing member.

At least one of the first polishing and the second polishing may becarried out while keeping a contact member, disposed in the vicinity ofthe processing electrode and/or the feeding electrode, in contact withthe surface of the metal film of the workpiece.

In a preferred embodiment of the present invention, the first polishingand the second polishing are carried out respectively by applying avoltage between a processing electrode, disposed close to or in contactwith the metal film of the workpiece, and a feeding electrode forfeeding electricity to the metal film, supplying a liquid between theworkpiece and at least one of the processing electrode and the feedingelectrode, and moving the workpiece relative to at least one of theprocessing electrode and the feeding electrode.

A resistance-forming processing may be carried out prior to orsimultaneously with the second polishing. Further, the second polishingmay be carried out while keeping the processing electrode contactlesswith the pattern region and simultaneously carrying out aresistance-forming processing of the pattern region.

At least one of the first polishing and the second polishing may becarried out while keeping a contact member, disposed in the vicinity ofthe processing electrode and/or the feeding electrode, in contact withthe surface of the metal film of the workpiece.

At least one of the first polishing and the second polishing may also becarried out while keeping the processing electrode at a distance of 0.05to 50 μm from the surface of the metal film of the workpiece.

The use of an ionic reaction promoter in combination with the use of aliquid having an electric conductivity of not more than 500 μS/cm makesit possible to carry out the first polishing while keeping theprocessing electrode at a distance of 0.05 to 50 μm from the surface ofthe metal film of the workpiece. The ionic reaction promoter can hinderadsorption of a substance, which acts as an insulating additive orpreservative used in resistance-forming processing and suppresses anelectrolytic processing, so as to maintain the electrolytic processing(reaction). As the ionic reaction promoter, organosulfur compoundscontaining sulfonic group represented by the bis(3-sulfopropyl)disulfideare suitably used. If a liquid having a high electric conductivity isused, polishing of the metal film will be isotropic both in the patternregion and in the field region, that is, there will be no significantdifference in the polishing rate of the metal film between the patternregion and the field region. The use of a liquid having a low electricconductivity can make the polishing of the metal film anisotropic andproduce a difference in the polishing rate of the metal film between thepattern region and the field region. The ionic reaction promoter can beconcentrated at portions of high electric field intensity, i.e. the topportions of the raised portions of the metal film in the pattern region.This can increase the polishing rate of the metal film in the patternregion. It has been confirmed experimentally that when carrying outelectrolytic processing while changing a distance between a processingelectrode and a metal film, the metal film can be polished desirablywhen the distance is kept between 0.05 μm and 50 μm.

The end point of the first polishing can be detected by time management,detection of a table current, or image recognition.

The time management refers to processing time management, that is, thefirst processing is terminated after an elapse of the predeterminedprocessing time which is determined based on a current condition.

The pattern of the pattern region, i.e. the surface irregularities ofthe metal film, is removed gradually with the progress of the firstpolishing. A point of time, at which the surface irregularities havebeen substantially removed or flattened, is regarded as the end point ofthe first polishing. For example, when polishing a metal film surfacewhile keeping a processing member in contact with the metal film, as themetal film surface becomes flattened with the progress of polishing, thecontact area between the metal film and the processing member becomeslarger, whereby the table current becomes higher. The progress ofpolishing of the metal film can also be perceived by the change in thepattern image gradually disappearing. Thus, the end point of the firstpolishing can be detected by the detection of table current or by imagerecognition.

The present invention provides another flattening apparatus comprising:a first polishing section for polishing a surface of a metal film,formed on a workpiece and having a pattern region and a field region, insuch a manner that the polishing rate of the metal film in the patternregion is higher than the polishing rate of the metal film in the fieldregion; and a second polishing section for polishing the metal filmsurface in such a manner that the polishing rate of the metal film inthe field region is higher than the polishing rate of the metal film inthe pattern region.

Preferably, at least one of the first polishing section and the secondpolishing section carries out polishing by electrolytic processing.

BRIEF DESCRIPTION OF DRAWINGS

FIGS. 1A through 1C are diagrams illustrating, in a sequence of processsteps, an example for the production of a substrate having copperinterconnects;

FIGS. 2A through 2D are diagrams illustrating processing of a copperfilm as an interconnect material by a conventional electrolyticprocessing method;

FIGS. 3A through 3C are another diagrams illustrating polishing of acopper film as an interconnect material by a conventional electrolyticprocessing method;

FIGS. 4A through 4C are diagrams illustrating polishing of a copper filmas an interconnect material ideally by a electrolytic processing method;

FIG. 5 is a layout plan view of a flattening apparatus according to anembodiment of the present invention;

FIG. 6 is a schematic view of a resist processing apparatus (coatingmaterial processing apparatus) of the flattening apparatus shown in FIG.5;

FIGS. 7A through 7C are diagrams illustrating coating of recessedportions of a copper film with a coating material by the resistprocessing apparatus shown in FIG. 6;

FIG. 8 is a plan view of an electrolytic processing apparatus of theflattening apparatus shown in FIG. 5;

FIG. 9 is a vertical sectional view of the electrolytic processingapparatus shown in FIG. 8;

FIG. 10 is a vertical sectional view of an electrode section of theelectrolytic processing apparatus shown in FIG. 8;

FIG. 11 is a cross-sectional view of the main portion of the electrodesection of the electrolytic processing apparatus shown in FIG. 8,illustrating processing of a substrate with the electrode section;

FIGS. 12A through 12D are diagrams illustrating processing of a copperfilm as an interconnect material by a flattening method according to anembodiment of the present invention;

FIG. 13 is a schematic view of another resist processing apparatus;

FIGS. 14A and 14B are diagrams illustrating coating of recessed portionsof a copper film with a coating material by the resist processingapparatus shown in FIG. 13;

FIGS. 15A through 15D are diagrams illustrating processing of a copperfilm as an interconnect material by a flattening method according toanother embodiment of the present invention;

FIG. 16 is a cross-sectional view of the main portion of anotherelectrode section of the electrolytic processing apparatus;

FIG. 17 is a layout plan view of a flattening apparatus according toanother embodiment of the present invention;

FIG. 18 is a plan view of an electrolytic processing apparatus of theflattening apparatus shown in FIG. 17;

FIG. 19 is a cross-sectional view of the main portion of a firstelectrode section (first polishing section) of the electrolyticprocessing apparatus shown in FIG. 18, illustrating processing of asubstrate with the first electrode section;

FIG. 20 is a cross-sectional view of the main portion of a secondelectrode section (second polishing section) of the electrolyticprocessing apparatus shown in FIG. 18, illustrating processing of asubstrate with the second electrode section;

FIGS. 21A through 21C are diagrams illustrating processing of a copperfilm as an interconnect material by a flattening method according to yetanother embodiment of the present invention;

FIG. 22 is a diagram schematically showing a coated surface of a copperfilm in a pattern region with an additive (insulating material);

FIG. 23 is a graph showing a relationship between a table current andpolishing time when carrying out a first polishing of the presentinvention; and

FIGS. 24A and 24B are diagrams illustrating the change of the patternwith the progress of the first polishing.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be described indetail with reference to the drawings. The following descriptionillustrates the case of using a substrate as a workpiece, and processingand flattening the surface of a metal film (conductive film) as aprocessing object, in particular, a copper film 6 (see FIG. 1B) formedas an interconnect material on the substrate. The present invention is,of course, applicable to flattening of a workpiece other than asubstrate, or a metal film (conductive film) other than a copper film.

FIG. 5 is a plan view illustrating a flattening apparatus according toan embodiment of the present invention. As shown in FIG. 5, theflattening apparatus comprises a pair of loading/unloading units 30 as acarry-in and carry-out section for carrying in and carrying out acassette housing a substrate W, e.g. a substrate W, as shown in FIG. 1B,which has in its surface a copper film 6 as a metal film (conductivefilm) to be processed, a reversing machine 32 for reversing thesubstrate W, a resist processing apparatus 34, as a coating materialprocessing apparatus, for coating a resist as a coating material on asurface of the substrate W and exposing the resist, an electrolyticprocessing apparatus 36 for performing electrolytic processing using noabrasive, and a cleaning section 38 for cleaning and drying theprocessed substrate. These devices are disposed in series. A transportrobot 40 as a transport device, which can move parallel to these devicesfor transporting and transferring the substrate W therebetween, isprovided. The flattening apparatus is also provided with a monitor 42,adjacent to the loading/unloading units 30, for monitoring a voltageapplied between the below-described processing electrodes and thefeeding electrodes during electrolytic processing in the electrolyticprocessing apparatus 36, or an electric current flowing therebetween.

FIG. 6 shows the resist processing apparatus (coating materialprocessing apparatus) 34 in the flattening apparatus. As shown in FIG.6, the resist processing apparatus 34 mainly comprises a resistapplication section 50 and an exposure section 52. The resistapplication section 50 includes a rotatable substrate stage 54 fordetachably holding the substrate W with its front surface, i.e. thesurface having the copper film 6 (see FIG. 1B), facing upward, a pivotarm 56 pivotably disposed above the substrate stage 54, and a resistdropping nozzle 58 which is mounted to the free end of the pivot arm 52and moves between a processing position almost above the center of thesubstrate W held on the substrate stage 54 and a retreat position besidethe substrate W. The exposure section 58 has a built-in ultraviolet lamp60 and is disposed right above the substrate stage 54. Further, thoughnot shown diagrammatically, the resist processing apparatus 34 alsoincludes a development section for supplying a developer to the surfaceof the substrate W to develop the exposed resist, and a cleaning sectionfor cleaning the substrate surface after development. If necessary, aheater stage for baking the resist e.g. at 100 to 150° C. after thecleaning of the substrate may be provided, for example, beside theresist processing apparatus 34.

According to this embodiment, a positive photoresist of insulatingmaterial, having a resistivity of not less than 10⁶ Ω·cm (electricconductivity of not more than 1 μS/cm), is used as a coating material toform a coating layer, and the positive photoresist 62 is applied to thesurface of the substrate W. Resists include, besides photoresists, X-rayresists and electron beam resists, which are each sensitive to lighthaving a particular wavelength range. Any resist can be used in thepresent invention. Further, resists can be classed into the positivetype and the negative type according to whether the exposed portion orthe non-exposed portion is dissolved by development. Though aphotoresist of the positive type is used in this embodiment, a negativeresist may also be used. Instead of a resist, it is also possible to usea paint, an oil-based ink (permanent marker), a quick-drying adhesive,etc.

The operation of the resist processing apparatus 34 will now bedescribed with reference to FIGS. 7A through 7C. First, a substrate W isheld with its front surface facing upward on the upper surface of thesubstrate stage 54. The resist dropping nozzle 58 in the retreatposition beside the substrate stage 54 is moved to the processingposition almost above the center of the substrate W held on thesubstrate stage 54. The positive photoresist 62 is then dropped from theresist dropping nozzle 58 onto almost the center of the substrate Wwhile rotating the substrate W together with the substrate stage 54 tospin-coat the substrate W, thereby applying the positive photoresist 62uniformly onto the surface of copper film 6 while filling the positivephotoresist 62 into the recessed portions 6 a of the copper film (metalfilm) 6 which fills trenches 4 provided in an insulating film 2 andcovers the insulating film 2, as shown in FIG. 7A.

Next, after moving the resist dropping nozzle 58 from the processingposition to the retreat position, the surface of the substrate W isirradiated with ultraviolet rays emitted from the ultraviolet lamp 60 ofthe exposure section 52, thereby exposing the resist 62 a other than theresist 62 b lying at the bottoms of the recessed portions 6 a of thecopper film 6, as shown in FIG. 7B. Thereafter, a developer is suppliedto the surface of the substrate W to develop and remove the exposedresist 62 a, thereby coating the recessed portions 6 a of the copperfilm 6 with a coating layer (insulating layer) composed of the resist(coating material) 62 (62 b) of insulating material.

Thereafter, the surface of the substrate W is cleaned (rinsed) e.g. withpure water and, if necessary, the substrate W is subjected to bakinge.g. at 100 to 150° C. By baking the resist 62 and causing the solventin the resist 62 to evaporate, the removal rate of the resist 62 in thebelow-described electrolytic processing can be changed. Thus, byutilizing this and adjusting the baking temperature and the baking time,it becomes possible to control the selectivity ratio between the copperfilm (metal film) 6 and the resist 62 in electrolytic processing toflatten the copper film 6. In general, baking at a higher temperaturefor a longer time results in a slower processing rate of resist.

FIG. 8 is a plan view schematically showing the electrolytic processingapparatus 36 shown in FIG. 5, and FIG. 9 is a vertical sectional view ofFIG. 8. As shown in FIGS. 8 and 9, the electrolytic processing apparatus36 includes an arm 240 that can move vertically and make a reciprocationmovement in a horizontal plane, a substrate holder 242, supported at thefree end of the arm 240, for attracting and holding the substrate W withits front surface facing downward (face-down), and a moveable flame 244to which the arm 240 is attached.

A vertical-movement motor 250 is mounted on the upper end of themoveable flame 244. A ball screw 252, which extends vertically, isconnected to the vertical-movement motor 250. The base 240 a of the arm240 is engaged with the ball screw 252, and the arm 240 moves up anddown via the ball screw 252 by the actuation of the vertical-movementmotor 250. The moveable flame 244 is connected to a ball screw 254 thatextends horizontally, and moves back-and-forth in a horizontal planewith the arm 240 by the actuation of a reciprocating motor 256.

The substrate holder 242 is connected to a rotating motor 258 supportedat the free end of the arm 240. The substrate holder 242 is rotated(about its own axis) by the actuation of the rotating motor 258. The arm240 can move vertically and make a reciprocation movement in thehorizontal direction, as described above, the substrate holder 242 canmove vertically and make a reciprocation movement in the horizontaldirection integrated with the arm 240.

A rectangular electrode section 246 is disposed below the substrateholder 242. The electrode section 246 is designed to have a slightlylarger size than the diameter of the substrate W to be held by thesubstrate holder 242.

The hollow motor 260 is disposed below the electrode section 246. Adrive end 264 is formed at the upper end portion of the main shaft 262of the hollow motor 260 and arranged eccentrically position to thecenter of the main shaft 262. The electrode section 246 is rotatablycoupled to the drive end 264 via a bearing (not shown) at the centerportion thereof. Three or more of rotation-prevention mechanisms (notshown) are provided in the circumferential direction between theelectrode section 246 and the hollow motor 260. This allows theelectrode section 246 make a scroll movement (translational rotationmovement) by the actuation of a hollow motor 260.

Next, the electrode section 246 will now be described in detail. FIG. 10is a vertical sectional view of the electrode section 246. As shown inFIGS. 8 and 10, the electrode section 246 includes a plurality ofelectrode members 282 which extend in the X direction (see FIG. 8) andare disposed in parallel at an even pitch on a tabular processing table284.

As shown in FIG. 10, each electrode member 282 comprises an electrode286 to be connected to the power source 248 (see FIG. 8), and an ionexchanger 290 that serves as a processing member and covers a surface ofthe electrode 286 integrally. The ion exchanger 290 is mounted to theelectrode 286 via holding plates 285 disposed on both sides of theelectrode 286.

According to this embodiment, an ion exchanger is used as a processingmember. A processing member may be composed of a material containing anion exchange, a polishing pad such as a polyurethane form pad, e.g.,IC-1000 manufactured by Rohm and Haas Electronic Materials, Inc, afixed-abrasive pad, or a PVA sponge.

It is preferable to use an ion exchanger having good water permeabilityas the ion exchanger 290. By allowing pure water or ultrapure water toflow within the ion exchanger 290, a sufficient amount of water can besupplied to a functional group (sulfonic acid group in the case of anion exchanger carrying a strongly acidic cation-exchange group) therebyto increase the amount of dissociated water molecules, and the processproduct (including a gas) formed by the reaction with hydroxide ions (orOH radicals) can be removed by the flow of water, whereby the processingefficiency can be enhanced. A water-permeable sponge-like member or amember in the form of a membrane, such as Nafion (trademark, DuPontCo.), having through-holes for permitting water to flow therethrough,for example, is used as such a water-permeable member.

The ion exchanger 290 may be composed of a non-woven fabric which has ananion-exchange group or a cation-exchange group. A cation exchangerpreferably carries a strongly acidic cation-exchange group (sulfonicacid group); however, a cation exchanger carrying a weakly acidiccation-exchange group (carboxyl group) may also be used. Though an anionexchanger preferably carries a strongly basic anion-exchange group(quaternary ammonium group), an anion exchanger carrying a weakly basicanion-exchange group (tertiary or lower amino group) may also be used.The base material of the ion exchanger 290 may be a polyolefin such aspolyethylene or polypropylene, or any other organic polymer. Further,besides the form of a non-woven fabric, the ion exchanger may be in theform of a woven fabric, a sheet, a porous material, a net, or shortfibers, etc. A strongly acidic cation-exchange fiber (non-woven fabricion exchanger) may be disposed inside the ion exchanger 290 to enhancean ion exchange capacity.

The non-woven fabric carrying a strongly basic anion-exchange group canbe prepared by, for example, the following method: A polyolefinnon-woven fabric having a fiber diameter of 20-50 μm and a porosity ofabout 90% is subjected to the so-called radiation graft polymerization,comprising γ-ray irradiation onto the non-woven fabric and thesubsequent graft polymerization, thereby introducing graft chains; andthe graft chains thus introduced are then aminated to introducequaternary ammonium groups thereinto. The capacity of the ion-exchangegroups introduced can be determined by the amount of the graft chainsintroduced. The graft polymerization may be conducted by the use of amonomer such as acrylic acid, styrene, glicidyl methacrylate,chloromethylstyrene, or the like. The amount of the graft polymerizationcan be controlled with adjusting the monomer concentration, the reactiontemperature and the reaction time. Thus, the degree of grafting, i.e.the ratio of the weight of the non-woven fabric after graftpolymerization to the weight of the non-woven fabric before graftpolymerization, can be made 500% at its maximum. Consequently, thecapacity of the ion-exchange groups introduced after graftpolymerization can be made 5 meq/g at its maximum.

The non-woven fabric carrying a strongly acidic cation-exchange groupcan be prepared by the following method: As in the case of the non-wovenfabric carrying a strongly basic anion-exchange group, a polyolefinnon-woven fabric having a fiber diameter of 20-50 μm and a porosity ofabout 90% is subjected to the so-called radiation graft polymerizationcomprising γ-ray irradiation onto the non-woven fabric and thesubsequent graft polymerization, thereby introducing graft chains; andthe graft chains thus introduced are then treated with a heated sulfuricacid to introduce sulfonic acid groups thereinto. If the graft chainsare treated with a heated phosphoric acid, phosphate groups can beintroduced. The degree of grafting can reach 500% at its maximum, andthe capacity of the ion-exchange groups thus introduced after graftpolymerization can reach 5 meq/g at its maximum.

The base material of the ion exchanger 290 may be a polyolefin such aspolyethylene or polypropylene, or any other organic polymer. Further,besides the form of a non-woven fabric, the ion exchanger 290 may be inthe form of a woven fabric, a sheet, a porous material, or short fibers,etc. When polyethylene or polypropylene is used as the base material,graft polymerization can be effected by first irradiating radioactiverays (γ-rays or electron beam) onto the base material (pre-irradiation)to thereby generate a radical, and then reacting the radical with amonomer, whereby uniform graft polymer with few impurities can beobtained. When an organic polymer other than polyolefin is used as thebase material, on the other hand, radical polymerization can be effectedby impregnating the base material with a monomer and irradiatingradioactive rays (γ-rays, electron beam and UV-rays) onto the basematerial (simultaneous irradiation). Though this method fails to provideuniform graft chains, it is applicable to a wide variety of basematerials.

By using a non-woven fabric having an anion-exchange group or acation-exchange group as the ion exchanger 290, it becomes possible thata liquid, such as pure water or ultrapure water, can freely move withinthe non-woven fabric and easily arrive at the active points in thenon-woven fabric having a catalytic activity for water dissociation, sothat many water molecules are dissociated into hydrogen ions andhydroxide ions. Further, by the movement of the liquid, such as purewater or ultrapure water, the hydroxide ions produced by the waterdissociation can be efficiently carried to the surfaces of theelectrodes 286, whereby a high electric current can be obtained evenwith a low voltage applied.

When the ion exchangers 290 have only one of anion-exchange groups andcation-exchange groups, a limitation is imposed on electrolyticallyprocessable materials and, in addition, impurities are likely to formdue to the polarity. In order to solve this problem, an anion exchangercarrying an anion-exchange group and a cation exchanger carrying acation-exchange group may be superimposed, or the ion exchangers 290 maycarry both of an anion-exchange group and a cation-exchange group perse, whereby a range of materials to be processed can be broadened andthe formation of impurities can be restrained.

According to this embodiment, the electrodes 286 of the electrodemembers 282 are connected alternately to the cathode and to the anode ofthe power source 248. For example, electrodes 286 a (see FIG. 10) areconnected to the cathode of the power source 248, and electrodes 286 b(see FIG. 10) are connected to the anode. When processing copper, forexample, the electrolytic processing action occurs on the cathode side,and therefore the electrodes 286 connected to the cathode becomeprocessing electrodes 286 a, and the electrodes 286 connected to theanode become feeding electrodes 286 b. Thus, according to thisembodiment, the processing electrodes 286 a and the feeding electrodes286 b are disposed in parallel and alternately.

Depending upon the material to be processed, the electrodes connected tothe cathode of the power source may serve as feeding electrodes, and theelectrodes connected to the anode may serve as processing electrodes.Thus, when the material to be processed is copper, molybdenum or iron,for example, the electrolytic processing action occurs on the cathodeside, and therefore electrodes 286 a connected to the cathode of thepower source becomes processing electrodes, and electrodes 286 bconnected to the anode becomes feeding electrodes. On the other hand,when the material to be processed is aluminum or silicon, for example,the electrolytic processing action occurs on the anode side, andtherefore the electrodes 286 b connected to the anode of the powersource become processing electrodes and the electrodes 286 a connectedto the cathode become feeding electrodes.

By thus providing the processing electrodes 286 a and the feedingelectrodes 286 b alternately in the Y direction of the electrode section246 (direction perpendicular to the long direction of the electrodemember 282), provision of a feeding section for feeding electricity tothe copper film (metal film) 6 (see FIG. 1B) of the substrate W is nolonger necessary, and processing of the entire surface of the substrateW becomes possible. Further, by changing the positive and negative ofthe voltage applied between the electrodes 286 in a pulse form, itbecomes possible to dissolve the electrolysis products, and improve theflatness of the processed surface through the multiplicity of repetitionof processing.

With respect to the electrodes 286 of the electrode members 282,oxidation or dissolution thereof due to an electrolytic reaction may bea problem. In view of this, as a material for the electrodes, it ispossible to use, besides the conventional metals and metal compounds,carbon, relatively inactive noble metals, conductive oxides orconductive ceramics, preferably. A noble metal-based electrode may, forexample, be one obtained by plating or coating platinum or iridium ontoa titanium electrode, and then sintering the coated electrode at a hightemperature to stabilize and strengthen the electrode. Ceramics productsare generally obtained by heat-treating inorganic raw materials, andceramics products having various properties are produced from variousraw materials including oxides, carbides and nitrides of metals andnonmetals. Among them there are ceramics having an electricconductivity. When an electrode is oxidized, the value of the electricresistance generally increases to cause an increase of applied voltage.However, by protecting the surface of an electrode with a non-oxidativematerial such as platinum or with a conductive oxide such as an iridiumoxide, the decrease of electric conductivity due to oxidation of thebase material of an electrode can be prevented.

As shown in FIG. 10, a flow passage 292, for supplying pure water,preferably ultrapure water, to the processing surface, is provided inthe interior of the processing table 284 of the electrode section 246.The flow passage 292 is connected, via a pure water supply tube 294, toa pure water supply source (not shown). Support members 296 are providedon both sides of each electrode member 282, and contact member 298, forcontacting the surface (lower surface) of the substrate W, is providedon the upper surface of each support member 296. A through-hole 296 a,communicating with the flow passage 292, is formed in the support member296 and the contact member 298, so that pure water, preferably ultrapure water, is supplied through the through-holes 296 a to between thesubstrate W and the ion exchangers 290 of the electrode members 282.

A CMP pad, a fixed-abrasive pad, a PVA sponge, etc. can be used as thecontact member 298. An ion exchanger or a material containing an ionexchanger may also be used.

According to this electrolytic processing apparatus 36, as shown in FIG.11, the substrate W is brought into contact with the upper surfaces ofthe contact members 298 while pressing the substrate W against the ionexchangers 290 at a certain degree of pressure. Thus, the pressing forceof the substrate W is received by the contact members 298 so that thecontact area between the substrate W and the ion exchangers 290 does notchange. This can prevent the substrate W from tilting and equalize thecontact areas, enabling uniform processing. The processing rate of thecoating material, such as resist, can be adjusted with contact members298.

Through-hole 300, which extends from the flow passage 292 and reaches tothe ion exchanger 290, is provided in the interior of the electrode 286of each electrode members 282. With this arrangement, a liquid, such aspure water or ultrapure water, in the flow passage is supplied to theion exchangers 290 via Through-holes 300.

The present invention is not limited to electrolytic processing using anion exchanger. For example, when an electrolytic solution is employed asa processing liquid, it is possible to attach to the surface of anelectrode a processing member other than an ion exchanger, such as asoft polishing pad or a non-woven fabric.

In operation of the electrolytic processing apparatus 36, the substrateW held by the substrate holder 242 is brought into contact with thesurfaces of the ion exchangers 290 of the electrode section 246 andupper surfaces of the contact members 298, as shown in FIG. 11. In thisstate, the substrate W held by substrate holder 242 is rotated and theelectrode section 246 is allowed to make a scroll movement by theactuation of the hollow motor 260, while pure water or ultrapure wateris supplied between the substrate W and the electrode members 282 viathrough-holes 296 a of the support members 296. Pure water or ultra purewater supplied via through-holes 300 of the electrode members 290 isheld in the ion exchangers 290. According to the embodiment, pure wateror ultrapure water supplied to the ion exchangers 290 is discharged fromthe ends in the long direction of each electrode member 282. A givenvoltage is applied from the power source 248 to between the processingelectrodes 286 a and the feeding electrodes 286 b, thereby carrying outelectrolytic processing of the copper film (metal film 6) deposited onthe surface of the substrate W.

A description will now be given of electrolytic processing by theflattening apparatus of this embodiment. First, a cassette housingsubstrates W, each having a surface copper film 6 as a metal film to beprocessed, which fills trenches 4 formed in an insulating film 2 andcovers the surface of the insulating film 2, as shown in FIG. 1B, is setin the loading/unloading section 30, and one substrate W is taken by thetransport robot 40 out of the cassette. As shown in FIG. 12A, the copperfilm 6 has a pattern region P with a large number of recessed portions 6a and raised portions 6 b, and a field region F surrounding the patternregion P. The transport robot 40 transports the substrate W to theresist processing apparatus (coating material processing apparatus) 34.In the resist processing apparatus 34, the recessed portions 6 a of thecopper film 6 are coated with the coating layer (insulating layer)composed of the resist (coating material) 62 of insulating material inthe above-described manner, according to this embodiment. Thereafter,the resist 62 is subjected to baking at a predetermined temperature fora predetermined time in order to adjust the removal rate of resist 62 inelectrolytic processing.

The transport robot 40 receives the substrate W after baking from theresist processing apparatus 34 and, as necessary, transports thesubstrate W to the reversing machine 32, where the substrate W isreversed so that its front surface having the copper film 6 facesdownward.

The transport robot 40 receives the reversed substrate W and transportsit to the electrolytic processing apparatus 36, where the substrate W isattracted and held by the substrate holder 242. Next, thevertical-movement motor 250 is actuated to lower the substrate holder242 so as to bring the substrate W held by the substrate holder 242 intocontact with the contact members 298 and the ion exchangers 290 of theelectrode section 246. Thereafter, the rotating motor 258 is actuated torotate the substrate W and, at the same time, the hollow motor 260 isactuated to allow the electrode section 246 to make a scroll movementwhile pure water or ultrapure water is supplied between the substrate Wand the ion exchangers 290.

A given voltage is applied from the power source 248 to between theprocessing electrodes 286 a and the feeding electrodes 286 b to carryout electrolytic processing at the processing electrodes (cathodes) 286a by the actuation of hydrogen ions or hydroxide ions produced by theion exchangers 290. The recessed portions 6 a in the pattern region P ofthe copper film 6 is coated with the resist (coating material) 62 whichis an insulating material and thus is hard to process by electrolyticprocessing. Accordingly, those portions of the copper film 6, which arenot coated with the resist (coating material) 62, are preferentiallyprocessed in the electrolytic processed, whereby the surface of thecopper film 6 is gradually flattened.

In particular, when electrolytic processing of the copper film 6, whichfills the trenches 4 formed in the insulating film 2 and covers thesurface of the insulating film 2, is carried out with the bottoms of therecessed portions 6 a in the pattern region P of the copper film 6coated with the resist (coating material) 62 of insulating material, asshown in FIG. 12A, the raised portions 6 b in the pattern region P ofthe copper film 6 are first preferentially processed, whereby thepattern region P is gradually flattened, as shown in FIG. 12B. Asprocessing further progresses, processing of the copper film 6 in thepattern region P is suppressed and the copper film 6 in the field regionF is preferentially processed, whereby the pattern region P and thefield region F are flattered with the resist (coating material) 62 ofinsulating material slightly left in the recessed portions 6 a in thepattern region P of the copper film 6, as shown in FIG. 12C. Asprocessing further progresses, the resist 62 remaining in the recessedportions 6 a in the pattern region P of the copper film 6 is removed andthe surface of the copper film 6 is flattened, as shown in FIG. 12D.

By using as the resist 62 to form a coating layer (insulating layer) amaterial which is highly adhesive to the copper film 6 and does notseparate from the copper film 6 even when carrying out electrolyticprocessing by applying such a high voltage as not less than 10V betweenthe processing electrodes 286 a and the feeding electrodes 286 b, asufficiently high processing rate can be obtained while maintaining theelectrolytic reaction-suppressing effect of the resist 62.

As will be appreciated from the foregoing, it is preferred that acoating material, such as the resist 62, of insulating material, have acertain degree of processability and be electrolytically processed at aslower rate than a metal film, such as the copper film 6. By adjustingthe selectivity ratio between the processing rate of resist 62 and theprocessing rate of copper film 6 in electrolytic processing, the surfaceof the copper film 6 can be flattened without leaving the resist 62 onthe copper film 6.

As described above, the processing rate of the resist (coating material)62 can be adjusted also by moving the copper film 6 and the contactmembers 298 relative to each other while keeping them in contact so asto rub off the surface of the coating material with the contact members298. This holds also for the below-described embodiments.

According to this embodiment, the copper film 6 and the resist 62 areprocessed in a continuous manner to flatten the surface of the copperfilm 6 without leaving the resist 62. However, there is a case where forsome reason, for example due to the processing rate of the resist 62, itis difficult to flatten the surface of the copper film 6 without leavingthe resist 62 by continuous processing. In such a case, it is possibleto remove the resist 62 in a separate process, for example, when thesurface of the copper film 6 is flattened both in the pattern region Pand in the field region F and the resist 62 has become exposed on thesurface of the copper film 6, as shown in FIG. 12C, and then furtherprocess the surface of the copper film 6, thereby flattening the surfaceof the copper film 6 without leaving the resist 62, as shown in FIG.12D. The processing after the removal of the resist 62 may be carriedout by electrolytic processing using, for example, an electrolyticsolution or ultrapure water, or by any other conventional method such asCMP.

As described above, it is also possible to remove the resist 62, whichis exposed on the surface of the copper film 6, as shown in FIG. 12C,with the contact members 298 by moving the copper film 6 and the contactmembers 298 relative to each other while keeping them in contact.

After the completion of electrolytic processing, the processingelectrodes 286 a and the feeding electrodes 286 b are disconnected fromthe power source 248, and the rotation of the substrate holder 242 andthe scroll movement of the electrode section 246 are stopped.Thereafter, the substrate holder 242 is raised, and the arm 240 is movedto transfer the substrate W to the transport robot 40. The transportrobot 40 transports the substrate W to the reversing machine 32 toreverse the substrate W, as necessary, and returns the substrate W tothe cassette of the loading/unloading section 30.

Pure water, which is supplied between the substrate W and the ionexchangers 290 during electrolytic processing, herein refers to a waterhaving an electric conductivity of not more than 10 μS/cm, for example.Ultrapure water refers to a water having an electric conductivity of notmore than 0.1 μS/cm, for example. The use of pure water or ultrapurewater containing no electrolyte during electrolytic processing canprevent extra impurities, such as an electrolyte, from adhering to andremaining on the surface of the substrate W. Further, copper ions or thelike dissolved during electrolytic processing are immediately caught bythe ion exchangers 290 through the ion-exchange reaction. This canprevent the dissolved copper ions or the like from re-precipitating onthe other portions of the substrate W, or from being oxidized to becomefine particles which contaminate the surface of the substrate W.

It is possible to use, instead of pure water or ultrapure water, aliquid having an electric conductivity of not more than 500 μS/cm e.g.,an electrolytic solution obtained by adding an electrolyte to pure wateror ultrapure water. The use of an electrolytic solution can furtherlower the electric resistance and reduce the power consumption. Asolution of a neutral salt such as NaCl or Na₂SO₄, a solution of an acidsuch as HCl or H₂SO₄, or a solution of an alkali such as ammonia, may beused as the electrolytic solution, and these solutions may beselectively used according to the properties of the workpiece.

Further, it is also possible to use, instead of pure water or ultrapurewater, a liquid obtained by adding a surfactant to pure water orultrapure water, and having an electric conductivity of not more than500 μS/cm, preferably not more than 50 μS/cm, more preferably not morethan 0.1 μS/cm (resistivity of not less than 10 MΩ·cm). Due to thepresence of a surfactant, the liquid can form a layer, which functionsto inhibit ion migration evenly, at the interface between the substrateW and the ion exchangers 290, thereby moderating concentration of ionexchange (metal dissolution) to enhance the flatness of the processedsurface. The surfactant concentration is desirably not more than 100ppm. When the value of the electric conductivity is too high, thecurrent efficiency is lowered and the processing rate is decreased. Theuse of the liquid having an electric conductivity of not more than 500μS/cm, preferably not more than 50 μS/cm, more preferably not more than0.1 μS/cm, can attain a desired processing rate.

FIG. 13 shows another resist processing apparatus as a coating materialprocessing apparatus. As shown in FIG. 13, the resist processingapparatus (coating material processing apparatus) 34 a comprises thesame resist application section 50 as used in the resist processingapparatus 34 shown in FIG. 6, and a resist wiping section 70. The resistwiping section 70 includes a rotary plate 72 rotatably and verticallymovably disposed above the substrate stage 54 of the resist applicationsection 50, and a wiping pad 74 mounted face down on the lower surfaceof the rotary plate 72.

According to this resist processing apparatus 34 a, while rotating asubstrate W together with the substrate stage 54, a resist 62 is droppedfrom the resist dropping nozzle 58 onto almost the center of thesubstrate W held face up on the upper surface of the substrate stage 54to spin-coat the substrate surface, thereby applying the resist 62uniformly onto the surface of a copper film (metal film) 6 while fillingthe resist 62 into the recessed portions 6 a of the copper film 6 whichfills trenches 4 provided in an insulating film 2 and covers theinsulating film 2, as shown in FIG. 14A. Next, the rotary plate 72 islowered while rotating it to rub the surface (lower surface) of thewiping pad 74 against the surface of the resist 62, thereby removing theresist 62 lying on the raised portions 6 b of the copper film 6 whileleaving the resist 62 lying within the recessed portions 6 a, as shownin FIG. 14B. Only the recessed portions 6 a of the copper film 6 arethus coated with a coating layer composed of the resist (coatingmaterial) 62.

When thus spin-coating the substrate why dropping the resist 62 onto thesurface of the substrate W and then rotating the substrate W, the resist62 is applied thicker on the recessed portions 6 a of the copper film 6than on the raised portions 6 b. For example, in the case of a patternhaving an interconnect width of 9 μm and a spacing of 1 μm, it ispossible to make the difference in the thickness of resist 62 betweenthe interconnect area and the spacing area not less than 400 nm.Accordingly, only the resist 62 lying on the raised portions 6 b of thecopper film 6 can be selectively removed by rubbing the surface (lowersurface) of the wiping pad 74 against the surface of the resist 62.

According to this embodiment, any resist other than a positivephotoresist can be used as a coating material.

As with the preceding embodiment, it is possible to provide a heaterstage e.g. beside the resist processing apparatus 34 a, and bake theresist 62 e.g. at 100 to 150° C. in order to adjust the removal rate ofthe resist 62 in electrolytic processing.

Though in this embodiment a resist of insulating material, having aresistivity of not less than 10⁶ Ω·cm (electric conductivity of not morethan 1 μS/cm), is used as a coating material to form a insulating layer(coating layer), it is also possible to use a conductive material havinga resistivity of not more than 10³ Ω·cm (electric conductivity of notless than 10³ μS/cm) to form a conductive layer (coating layer).Examples of the conductive material include a conductive paint, aconductive ink, a conductive adhesive and a conductive paste. Theseconductive materials can be prepared by mixing a resin with conductiveparticles, such as fine metal particles or carbon particles, and theconductivity can be adjusted by the mixing ratio of the conductiveparticles.

Also in the case of using a conductive material as a coating material64, the recessed portions 6 a of the copper film (metal film) 6, whichfills the trenches 4 provided in the insulating film 2 and covers thesurface of the insulating film 2, are first coated with the coatingmaterial 64, as shown in FIG. 15A. The coating may be carried out, forexample, by applying a conductive ink, such as a permanent marker, ontothe entire surface of the copper film 6, and then wiping off theconductive ink on the surface of the copper film 6 with an alcohol or athinner, or by selectively applying a conductive ink only onto therecessed portions 6 a of the copper film 6 by an ink jet method.

Thereafter, the substrate W, in which the recessed portions 6 a of thecopper film 6 are coated with a coating layer (conductive layer)composed of the coating material 64, is subjected to electrolyticprocessing to flatten the surface of the copper film 6. In the casewhere the raised portions 6 b of the copper film (metal film) 6 in thepattern region P protrude from the surface of the coating material 64,as shown in FIG. 15A, the raised portions 6 b and the copper film 6 ofthe field region F are preferentially processed, whereby the patternregion P and the field region F are flattened as shown in FIG. 15B. Asprocessing further progresses, electrolytic reaction occurs also at thesurface of the coating material 64 and an electron current flows throughthe coating material 64 also to the copper film 6 of the recessedportions 6 a. Therefore, the current density in the entire surface,including the coating material 64, of the copper film 6 becomes moreuniform, whereby the entire surface of the copper film 6 is processedmore uniformly, as shown in FIG. 15C. As processing further progresses,the coating material 64 remaining in the recessed portions 6 a in thepattern region P of the copper film 6 is removed and the surface of thecopper film 6 is flattened.

Also in this case, it is preferred that the coating material 64, whichis a conductive material, have a certain degree of processability and beelectrolytically processed at a slower rate than a metal film, such asthe copper film 6. By adjusting the selectivity ratio between theprocessing rate of coating material 64 and the processing rate of copperfilm 6 during electrolytic processing, the surface of the copper film 6can be flattened without leaving the coating material 64 on the copperfilm 6.

As with the above-described embodiment, it is also possible to removethe coating material 64 in a separate process, for example, when thecoating material 64 has become exposed on the surface of the copper film6, and then further process the surface of the copper film 6, or toremove the coating material 64, which has become exposed on the surfaceof the copper film 6, with the contact members 298 by moving the copperfilm 6 and the contact members 298 relative to each other while keepingthem in contact.

FIG. 16 shows the main portion of another electrode section of theelectrolytic processing apparatus. The electrode section 246 a of thiselectrolytic processing apparatus differs from the electrode section 246of the above-described electrolytic processing apparatus in thefollowing respects:

The electrode section 246 a includes a plurality of electrodes 302extending parallel to each other. The electrodes 302 are arranged inparallel at a given pitch on a tabular processing table in an exposedstate, i.e. without being covered with an ion exchanger or the like. Theelectrodes 302 are connected alternately to the cathode and to the anodeof a power source. When processing copper, for example, the electrodes302 a connected to the cathode of the power source serve as processingelectrodes and the electrodes 302 b connected to the anode serve asfeeding electrodes.

A flow passage for supplying a liquid (electrolytic liquid), such aspure water, to a processing surface is formed in the interior of theprocessing table of the electrode section 246 b, and the flow passage isconnected, via a liquid supply pipe, to a liquid supply source. Supportmembers 310 are provided on both sides of each electrode 302, and acontact member 312, for contacting a surface (lower surface) of asubstrate W, is provided on the upper surface of each support member310. A through-hole 314, communicating with the flow passage, is formedin the support member 310 and the contact member 312, and a through-hole316, communicating with the flow passage, is formed in the electrode302, so that the liquid, such as pure water, is supplied through thethrough-holes 314, 316 to between the substrate W and the electrodes302.

A CMP pad, a fixed-abrasive pad, a PVA sponge, etc. can be used as thecontact member 312. An ion exchanger or a material containing an ionexchanger may also be used.

Electrolytic processing with the electrode section 246 b is carried outwhile keeping the substrate W, held by the substrate holder 242 (seeFIGS. 8 and 9), in contact with the surfaces of the contact members 312.The distance D between the substrate W and the electrodes 302 duringelectrolytic processing is kept not less than 0.05 μm and not more than50 μm without contact therebetween.

During the electrolytic processing, pure water, ultrapure water or aliquid having an electric conductivity of not more than 500 μS/cm issupplied between the substrate W and the electrodes 302.

The present invention enables a simple flattening of a metal filmsurface at a high speed. In particular, a surface of a metal film(conductive film), e.g. a copper film as an interconnect material, canbe flatly processed over the entire film surface at a sufficiently highprocessing rate even when the metal film has initial surfaceirregularities.

FIG. 17 is a plan view illustrating a flattening apparatus according toanother embodiment of the present invention. As shown in FIG. 17, theflattening apparatus comprises a pair of loading/unloading units 130, areversing machine 132 for reversing the substrate W, an electrolyticprocessing apparatus 138 which has a first polishing section 134 and asecond polishing section 136 and serves as a polishing apparatus, and acleaning section 140 for cleaning and drying the substrate W afterelectrolytic processing. These devices are disposed in series. Atransport robot 142 as a transport device, which can move parallel tothese devices for transporting and transferring the substrate Wtherebetween, is provided. The flattening apparatus is also providedwith a control section 144, adjacent to the loading/unloading units 30,for monitoring a voltage applied between the processing electrodes andthe feeding electrodes or an electric current flowing therebetween, ordetecting a table current.

FIG. 18 is a plan view schematically showing the electrolytic processingapparatus (polishing apparatus) 138 shown in FIG. 17. As shown in FIG.18, the electrolytic processing apparatus 138 includes an arm 240 thatcan move vertically and make a reciprocation movement in a horizontalplane, a substrate holder 242, supported at the free end of the arm 240,for attracting and holding the substrate W with its front surface facingdownward (face-down), and a moveable flame 244 to which the arm 240 isattached, as with the electrolytic processing apparatus 36 shown inFIGS. 8 and 9.

A vertical-movement motor 250 is mounted on the upper end of themoveable flame 244 so that the arm 240 moves up and down by theactuation of the vertical-movement motor 250. The moveable flame 244 perse is connected to a ball screw 254, which extends horizontally, so thatthe moveable flame 244 and the arm 240 move back-and-forth in ahorizontal plane by the actuation of a reciprocating motor 256. Thesubstrate holder 242 is connected to a rotating motor 258 supported atthe free end of the arm 240. The substrate holder 242 is rotated (aboutits own axis) by the actuation of the rotating motor 258.

Below the substrate holder 242 are disposed a rectangular firstelectrode section 246 b which, together with the substrate holder 242,constitutes the first polishing section 134, and a rectangular secondelectrode section 246 c which, together with the substrate holder 242,constitutes the second polishing section 136. The substrate holder 242moves between a position right above the first electrode section 246 band a position right above the second electrode section 246 c.

As with the electrode section 246 of the electrolytic processingapparatus 36 shown in FIGS. 8 and 9, the first electrode section 246 band the second electrode section 246 c make a scroll movement(translational rotation) by the actuation of a hollow motor.

The first electrode section 246 b has the same construction as theelectrode section 246 of the electrolytic processing apparatus 36 shownin FIGS. 8 and 9. As shown in FIG. 19, the substrate W is brought intocontact with the upper surfaces of the contact members 298 whilepressing the substrate W against the ion exchangers 290, covering theelectrodes 286, at a certain degree of pressure. Thus, the pressingforce of the substrate W is received by the contact members 298 so thatthe contact area between the substrate W and the ion exchangers 290 doesnot change. This can prevent the substrate W from tilting and equalizethe contact areas, enabling uniform processing.

Each ion exchanger (processing members) 290 of the first electrodesection 246 b has an elasticity so that when the substrate W is pressedagainst the ion exchanger 290 at a certain degree of pressure and isbrought into contact with the upper surfaces of the contact members 298,the ion exchanger 290 contacts the surfaces of the raised portions 6 bof the copper film (metal film) 6 in the pattern region P, shown in FIG.21A, and can keep contacting the surfaces of the raised portions 6 bduring processing, thereby selectively polishing the raised portions 6 band flattening the surface of the copper film 6 in the pattern region P,as shown in FIG. 21B.

In the operation of the first polishing section 134 having such aconstruction, the substrate W held by the substrate holder 242 isbrought into contact with the upper surfaces of the contact members 298and also with the surfaces of the ion exchangers 290 of the firstelectrode section 246 b, as shown in FIG. 19, thereby bringing the ionexchangers 290 into contact with the surfaces of the raised portions 6 bof the copper film (metal film) 6 in the pattern region P, shown in FIG.21A. While rotating the substrate W held by the substrate holder 242 andallowing the first electrode section 246 b to make a scroll movement,pure water or ultrapure water is supplied from the through-holes 296 aof the support members 296 to between the substrate W and the electrodemembers 282, and pure water or ultrapure water is supplied through thethrough-holes 300 of the electrodes 286 into the ion exchangers 290. Agiven voltage is applied from the power source 248 (see FIG. 18) tobetween the processing electrodes 286 a and the feeding electrodes 286 bto carry out the first polishing (electrolytic processing) of the copperfilm (metal film) 6, deposited on the surface of the substrate W, at theprocessing electrodes (cathodes) 286 a by the action of hydrogen ions orhydroxide ions produced by the ion exchangers 290.

In the polishing, the intensity of electric field is higher in thepattern region P, in which raised portions are concentrated, than in thefield region F, and therefore the amount of reaction species ionssupplied is larger in the pattern region P than in the field region F,leading to a higher processing rate of the copper film 6 in the patternregion P than in the field region F.

It is also possible to use an electrolytic liquid prepared by adding anionic reaction promoter to pure water, ultrapure water or the like. Theionic reaction promoter will concentrate at portions of high electricfield intensity, i.e. the top portions of the raised portions 6 b of thecopper film 6 in the pattern region P, thus increasing the polishingrate of the raised portions 6 b of the copper film 6 in the patternregion P. This can provide a sufficiently high polishing (processing)rate ratio for the metal film 6 between the pattern region P and thefiled region F.

Particularly, the first polishing by the first polishing section 134 iscontinued until the initial surface irregularities of the copper film 6in the pattern region P are removed. When the polishing rate for thecopper film of the pattern region P in the first polishing is small, thethickness of the copper film 6, to be subjected to the second polishingto remove the surface level difference in the copper film 6 between thepattern region P and the field region F, becomes undesirably small. Itis, therefore, desirable to make the polishing rate in the firstpolishing of the copper film 6 of the pattern region P at least twicethe polishing rate of the copper film 6 of the field region F so as toproduce a larger surface level difference in the metal film between thepattern region P and the filed region F, i.e. produce a thicker copperfilm 6, in the first polishing. This can be met by adding an ionicreaction promoter to an electrolytic liquid (liquid), such as pure wateror ultrapure water.

FIG. 20 shows the main portion of the second electrode section 246 cthat constitutes the second polishing section 136. The second electrodesection 246 c differs from the first electrode section 246 b in that anion exchanger 290 a, which has high rigidity and shows little elasticdeformation, is used as a processing member, and that the height of thesupport member 296, having the contact member 298 mounted on the uppersurface, is made higher so that when the substrate W is brought intocontact with the upper surface of the contact member 298 at a certaindegree of pressure, the ion exchanger 290 a does not contact the surfaceof the copper film (metal film) 6 of the pattern region P, shown in FIG.21B. The ion exchanger 290 a may contact the surface of the copper film6 of the field region F.

In the operation of the second polishing section 136, the substrate Wheld by the substrate holder 242 is brought into contact with thesurfaces of the contact members 298 of the second electrode section 246c, as shown in FIG. 20. The ion exchangers 290 a do not contact thesurface of the copper film (metal film) 6 of the pattern region P, shownin FIG. 21B. The ion exchangers 290 a, however, may contact the surface(metal film) 6 of the field region F, shown in FIG. 21B.

As with the first polishing section 134, while rotating the substrate Wheld by the substrate holder 242 and allowing the second electrodesection 246 c to make a scroll movement, pure water or ultrapure wateris supplied between the substrate W and the electrode members 282, andpure water or ultrapure water is supplied into the ion exchangers 290 a.A given voltage is applied between the processing electrodes 286 a andthe feeding electrodes 286 b to carry out electrolytic processing(second polishing) of the copper film (metal film) 6, deposited on thesurface of the substrate W, at the processing electrodes (cathodes) 286a.

Since the ion exchangers 290 a are not in contact with the surface ofthe copper film (metal film) 6 of the pattern region P, shown in FIG.21B, during the polishing, the polishing rate of the copper film 6 ofthe pattern region P is lower than that of the field region F and thecopper film 6 of the field section F is selectively polished, wherebythe surface level difference in the copper film 6 between the patternregion P and the field region F is removed and the copper film 6 isflattened, as shown in FIG. 21C.

The surface of the copper film 6 can thus be flattened over the entiresurface of the substrate W by mainly removing the initial surfaceirregularities of the copper film 6 in the pattern region P by the firstpolishing, and then mainly removing the surface level difference in thecopper film 6 between the pattern region P and the field region F by thesecond polishing.

Upon the second polishing, a resistance-forming processing maypreferably be carried out to form a resistance on the surface of thecopper film 6 in the pattern region P, thereby decreasing the polishingrate of the copper film (metal film) 6 in the pattern region P andproducing a larger difference in the polishing rate between the fieldregion F and the pattern region P. An example of the resistance-formingprocessing involves the use of a processing liquid (electrolyticliquid), prepared by adding an oxidizing agent (H₂O₂, O₃, etc.) or acomplexing agent to pure water, ultrapure water or the like, so as topassivate or complex the surface of the copper film 6 in the patternregion P, thereby retarding reaction species ions reaching the surfaceof the copper film 6 in the pattern region P.

Another processing involves the use of a processing liquid (electrolyticliquid), prepared by adding an additive having insulating properties topure water, ultrapure water or the like, so as to coat the surface ofthe copper film 6 with the additive (insulating material) 10 in thepattern region P, as shown in FIG. 22, thereby preventing reactionspecies ions from reaching the surface of the copper film 6 in thepattern region P.

Yet another processing involves the use of a processing liquid(electrolytic liquid), prepared by adding an additive, for example acorrosion inhibitor such as BTA (benzotriazole), which inhibits reactionbetween reaction species ions and the copper film 6, to pure water,ultrapure water or the like, so as to inhibit the reaction itselfbetween the reaction species ions and the copper film 6.

Though such a processing, especially passivation or complexing of thesurface of the copper film 6, or coating of the copper film 6 with theadditive (insulating material) 10, is desirably effected only in thepattern region P, the processing may be effected also in the fieldregion F, provided that the resistance formed can be removed from thefield region F by the contact pressure of the ion exchangers (processingmembers) 290 a or the contact members 298. Since the ion exchangers 290a are kept contactless with the pattern region P during the secondpolishing, a resistance, such as a passive film, a complex or aninsulating material, which has been formed on the surface of the copperfilm 6 in the pattern region P, is not removed by its contact with theion exchangers 290 a. On the other hand, the resistance, such as apassive film, formed on the surface of the copper film 6 in the fieldregion F can be removed by the contact pressure of the contact members298 which are kept in contact with the field region F during the secondpolishing.

In the case of not providing the contact members 298, it is possible toallow the ion exchangers 290 a to be in contact with the field region Fduring the second polishing so as to remove the resistance, such as apassive film, formed on the surface of the copper film 6 in the filedregion F, by the contact pressure of the ion exchangers 290 a.

Though in this embodiment the resistance-forming processing in thepattern region P is carried out simultaneously with the secondpolishing, it may be carried out prior to the second polishing.

In the operation of the flattening apparatus of this embodiment, thesubstrate holder 242 holding the substrate W is moved to a firstpolishing position right above the first electrode section 246 b. Thesubstrate holder 242 is then lowered so as to bring the substrate W,held by the substrate holder 242, into contact with the surfaces of thecontact members 298 and the ion exchangers 290 of the first electrodesection 246 b, thereby bringing the ion exchangers 290 into contact withthe surfaces of the raised portions 6 b of the copper film (metal film)6 of the pattern region P, shown in FIG. 21A. Thereafter, while rotatingthe substrate W and allowing the first electrode section 246 b to make ascroll movement, pure water or ultrapure water, optionally containing anionic reaction promoter, is supplied between the substrate W and the ionexchangers 290.

A given voltage is applied from the power source 248 to between theprocessing electrodes 286 a and the feeding electrodes 286 b to carryout the first polishing (electrolytic processing) at the processingelectrodes (cathodes) 286 a by the action of hydrogen ions or hydroxideions produced by the ion exchangers 290, in such a manner that thepolishing rate of the copper film 6 in the pattern region P is higherthan the polishing rate of the copper film 6 in the field region F. Thefirst polishing is terminated when the raised portions 6 b of the copperfilm 6 in the pattern region P have been selectively polished and theinitial surface irregularities have been removed, as shown in FIG. 21B.

According to this embodiment, an electric current (table current), whichis fed to cause the scroll movement of the processing table 284, isdetected with the control section 144 to detect the end point of thefirst polishing. Specifically, as the surface irregularities of thecopper film 6 become smaller and flattened with the progress of thefirst polishing, the contact area between the copper film 6 and the ionexchangers (processing members) 290 becomes larger, whereby the tablecurrent becomes higher, as shown in FIG. 23. The endpoint of the firstpolishing can be determined by a point of time at which the tablecurrent detected has reached a predetermined value.

The end point of the first polishing may also be detected by imagerecognition. As the first polishing progresses, the pattern image of thesurface of the copper film 6 changes from a clear pattern image 12 asshown in FIG. 24A to a faint pattern image 12 as shown in FIG. 24B andgradually disappears. Accordingly, the end point of the first polishingcan be detected by image recognition of the copper film 6 beingprocessed by a camera disposed above the processing table 284 (see FIG.10), or by image recognition of the copper film 6 of a substrate W,which is made to overhang the processing table 284 during processing, bya camera disposed beside the processing table 284. Alternatively, theend point of the first polishing may be detected by time management.

After completion of the first polishing, the processing electrodes 286 aand the feeding electrodes 286 b of the first electrode section 246 bare disconnected from the power source 248, and the rotation of thesubstrate holder 242 and the scroll movement of the first electrodesection 246 b are stopped. The substrate holder 242 is raised and movedto a second polishing position right above the second electrode section246 c, and is then lowered so as to bring the substrate W, held by thesubstrate holder 242, into contact with the surfaces of the contactmembers 298 of the second electrode section 246 c. As shown in FIG. 20,however, the ion exchanger 290 a are not brought into contact with thesurface of the copper film (metal film) 6 of the pattern region P, shownin FIG. 21B. Thereafter, while supplying pure water or ultrapure water,optionally containing an oxidizing agent, a complexing agent or anadditive having insulating properties, between the substrate W and theion exchangers 290 a, the second polishing (electrolytic processing) ofthe surface of the copper film 6 is carried out in the same mannerdescribed above. The first polishing (electrolytic polishing) and thesecond polishing (electrolytic polishing) may also be carried out usingthe same electrode section.

Since the ion exchangers 290 a are not in contact with the surface ofthe copper film (metal film) 6 of the pattern region P, shown in FIG.21B, during the second polishing, the polishing rate of the copper film6 is decreased and lower in the pattern region P than in the fieldregion F. The polishing rate of the copper film (metal film) 6 in thepattern region P can be further decreased by optionally carrying out theresistance-forming processing to form a resistance on the surface of thecopper film 6 in the pattern region P. The copper film 6 of the fieldsection F is thus selectively polished, whereby the surface leveldifference in the copper film 6 between the pattern region P and thefield region F is removed and the surface of the copper film 6 isflattened, as shown in FIG. 21C.

The end point of the second polishing can be detected, for example, bydetermining the processing amount through detection of a change infrictional force due to the removal of the surface level difference.

After completion of the second polishing, the processing electrodes 286a and the feeding electrodes 286 b of the second electrode section 246 care disconnected from the power source 248, and the rotation of thesubstrate holder 242 and the scroll movement of the second electrodesection 246 c are stopped. Thereafter, the substrate holder 242 israised, and the arm 240 is moved to transfer the substrate W to thetransport robot 142. The transport robot 142 transports the substrate Wto the reversing machine 132 to reverse the substrate W, as necessary,and returns the substrate W to the cassette of the loading/unloadingsection 130.

Though in this embodiment the substrate holder 242 and the firstelectrode section 246 b constitute the first polishing section 134, andthe substrate holder 242 and the second electrode section 246 cconstitute the second polishing section 136, sharing the substrateholder 242, it is also possible to carry out the first polishing and thesecond polishing by using separate electrolytic processing apparatuses.

Further, it is possible to use a cartridge-type processing table andchange it for a new one during polishing while holding a substrate Wwith the substrate holder 242.

The first polishing and the second polishing may also be carried out byusing, as the first electrode section 246 b and the second electrodesection 246 c, the electrode section 246 a shown in FIG. 16 andsupplying different liquids (electrolytic liquids) between a substrate Wand the electrodes 302 which are kept at a distance D of 0.05 to 50 μmwithout contact therebetween.

In particular, in carrying out the first polishing, a processing liquidprepared by adding an ionic reaction promoter to e.g. pure water,ultrapure water or a liquid having an electric conductivity of not morethan 500 μS/cm, is supplied between a substrate W and the electrodes302. This makes it possible to carry out the first polishing with thepolishing rate of the copper film (metal film) 6 in the pattern regionP, shown in FIG. 21A, higher than the polishing rate of the copper film6 in the field region F. In this regard, if a liquid having a highelectric conductivity is used, polishing of the copper film 6 will beisotropic both in the pattern region P and in the field region F, thatis, there will be no significant difference in the polishing rate of thecopper film 6 between the pattern region P and the field region F. Theuse of a liquid having such a low electric conductivity as not more than500 μS/cm can make the polishing of the copper film 6 an isotropic andproduce a difference in the polishing rate of the copper film 6 betweenthe pattern region P and the field region F. Further, the ionic reactionpromoter can be concentrated at portions of high electric fieldintensity, i.e. the top portions of the raised portions 6 b of thecopper film 6 in the pattern region P. This can increase the polishingrate of the copper film 6 in the pattern region P.

In the second polishing, a processing liquid prepared by adding anoxidizing agent (H₂O₂, O₃, etc.) or a complexing agent, an additivehaving insulating properties, or an, additive which inhibits reactionbetween reaction species ions and the copper film 6, as necessary, toe.g. pure water, ultrapure water or a liquid having an electricconductivity of not more than 500 μS/cm, is supplied between thesubstrate W and the electrodes 302, thereby carrying outresistance-forming processing of the pattern region P simultaneouslywith the second polishing. The resistance-forming processing candecrease the polishing rate of the copper film (metal film) 6 in thepattern region P, shown in FIG. 21B, producing a larger difference fromthe polishing rate of the copper film 6 in the field region F.

If the resistance, such as passivation, complexing, or coating with anadditive (insulating material) is effected also on the surface of thecopper film 6 of the field region F, the resistance formed can beremoved from the field region F by the contact pressure of the contactmembers 312.

Also in this embodiment, while rotating the substrate W, held by thesubstrate holder 242 and kept in contact with the contact members 312 ofthe electrode section 246 a, and allowing the electrode section 246 a tomake a scroll movement, a processing liquid, e.g. a liquid (electrolyticliquid) having an electric conductivity of not more than 500 μS/cm,containing an ionic reaction promoter, is supplied between the substrateW and the electrodes 302, and a given voltage is applied between theprocessing electrodes 302 a and the feeding electrodes 302 b to carryout the first polishing of the copper film (metal film) 6, deposited onthe surface of the substrate W, at the processing electrodes (cathodes)302 a.

Thereafter, while rotating the substrate W, held by the substrate holder242 and kept in contact with the contact members 312 of the electrodesection 246 a, and allowing the electrode section 246 a to make a scrollmovement, a liquid (electrolytic liquid) having an electric conductivityof not more than 500 μS/cm, optionally containing an oxidizing agent, acomplexing agent, or an additive having insulating properties, or thelike, is supplied between the substrate W and the electrodes 302, and agiven voltage is applied between the processing electrodes 302 a and thefeeding electrodes 302 b to carry out the second polishing (electrolyticprocessing) of the copper film 6.

The present invention enables a simple flattening of a metal filmsurface. In particular, the surface of a metal film (conductive film),e.g. a copper film as an interconnect material, can be flatly processedover its entire surface even when the metal film has initial surfaceirregularities.

While the present invention has been described with reference to theembodiments thereof, it will be appreciated by those skilled in the artthat changes could be made to the embodiments within the technicalconcept of the present invention.

INDUSTRIAL APPLICABILITY

The present invention is useful for processing and flattening a surfaceof a metal film which has been formed on a surface of a substrate andembedded into fine interconnects recesses formed in the surface of thesubstrate.

1. A flattening method for processing and flattening a surface of ametal film formed on a workpiece and having initial surfaceirregularities, comprising: coating only recessed portions of theinitial surface irregularities of the metal film with a pasty coatingmaterial; and processing the surface of the metal film by electrolyticprocessing.
 2. The flattening method according to claim 1 furthercomprising removing the coating material which has not been processed bythe electrolytic processing and remains on the surface of the metalfilm, and further processing the surface of the metal film.
 3. Theflattening method according to claim 1, wherein the coating material isan insulating material having a resistivity of not less than 10⁶ Ω·cm ora conductive material having a resistivity of not more than 10³ Ω·cm. 4.The flattening method according to claim 1, wherein only the recessedportions of the initial surface irregularities of the metal film arecoated with the coating material by applying the coating material ontothe entire surface of the metal film, and then removing only the coatingmaterial lying on the raised portions of the initial surfaceirregularities.
 5. The flattening method according to claim 1, whereinonly the recessed portions of the initial surface irregularities of themetal film are coated with the coating material by selectively applyingthe coating material onto the recessed portions of the metal film. 6.The flattening method according to claim 1, wherein the processing ofthe surface of the metal film by the electrolytic processing is carriedout by: applying a voltage between a processing electrode, disposedclose to the metal film of the workpiece, and a feeding electrode forfeeding electricity to the metal film; supplying a liquid into the spacebetween the workpiece and at least one of the processing electrode andthe feeding electrode, in which space a processing member is present;and moving the workpiece relative to at least one of the processingelectrode and the feeding electrode.
 7. The flattening method accordingto claim 6, wherein the processing member is composed of an ionexchanger or a material containing an ion exchanger.
 8. The flatteningmethod according to claim 6, wherein the processing of the surface ofthe metal film by the electrolytic processing is carried out by bringinga contact member, disposed beside the processing electrode and/or thefeeding electrode, into contact with the metal film surface.
 9. Theflattening method according to claim 1, wherein the processing of thesurface of the metal film by the electrolytic processing is carried outby: applying a voltage between a processing electrode, disposed close tothe metal film of the workpiece, and a feeding electrode for feedingelectricity to the metal film; supplying a liquid between the workpieceand at least one of the processing electrode and the feeding electrode;and moving the workpiece relative to at least one of the processingelectrode and the feeding electrode.
 10. The flattening method accordingto claim 9, wherein the processing of the surface of the metal film bythe electrolytic processing is carried out by bringing a contact member,disposed beside the processing electrode and/or the feeding electrode,into contact with the metal film surface.
 11. A flattening apparatuscomprising: a coating material processing apparatus for coating onlyrecessed portions of initial surface irregularities of a metal film witha pasty coating material; and an electrolytic processing apparatus forprocessing the surface of the metal film by electrolytic processing. 12.The flattening apparatus according to claim 11, wherein the coatingmaterial processing apparatus comprises a resist processing apparatus.13. A flattening method for polishing and flattening a surface of ametal film formed on a workpiece and having a pattern region and a fieldregion, comprising: carrying out a first polishing of the metal filmsurface in such a manner that the polishing rate of the metal film inthe pattern region is higher than the polishing rate of the metal filmin the field region; and carrying out a second polishing of the metalfilm surface in such a manner that the polishing rate of the metal filmin the field region is higher than the polishing rate of the metal filmin the pattern region.
 14. The flattening method according to claim 13,wherein at least one of the first polishing and the second polishing iscarried out by electrolytic processing.
 15. The flattening methodaccording to claim 13, wherein the first polishing and the secondpolishing are carried out by: applying a voltage between a processingelectrode, disposed close to the surface of the metal film of theworkpiece, and a feeding electrode for feeding electricity to the metalfilm; supplying a liquid into the space between the workpiece and atleast one of the processing electrode and the feeding electrode, inwhich space a processing member is present, and moving the workpiecerelative to at least one of the processing electrode and the feedingelectrode.
 16. The flattening method according to claim 15, wherein theprocessing member is composed of an ion exchanger or a materialcontaining an ion exchanger.
 17. The flattening method according toclaim 15, wherein the first polishing is carried out while keeping theprocessing member in contact with the pattern region, and the secondpolishing is carried out while keeping the processing member contactlesswith the pattern region.
 18. The flattening method according to claim15, wherein the first polishing is carried out while keeping theprocessing member in contact with the pattern region, and aresistance-forming processing of the pattern region is carried out priorto or simultaneously with the second polishing.
 19. The flatteningmethod according to claim 15, wherein the second polishing is carriedout while keeping the processing member contactless with the patternregion and simultaneously carrying out a resistance-forming processingof the pattern region.
 20. The flattening method according to claim 15,wherein at least one of the first polishing and the second polishing iscarried out while keeping a contact member, disposed in the vicinity ofthe processing electrode and/or the feeding electrode, in contact withthe surface of the metal film of the workpiece.
 21. The flatteningmethod according to claim 13, wherein the first polishing and the secondpolishing are carried out respectively by: applying a voltage between aprocessing electrode, disposed close to or in contact with the metalfilm of the workpiece, and a feeding electrode for feeding electricityto the metal film; supplying a liquid between the workpiece and at leastone of the processing electrode and the feeding electrode; and movingthe workpiece relative to at least one of the processing electrode andthe feeding electrode.
 22. The flattening method according to claim 21,wherein a resistance-forming processing of the pattern region is carriedout prior to or simultaneously with the second polishing.
 23. Theflattening method according to claim 21, wherein the second polishing iscarried out while keeping the processing electrode contactless with thepattern region and simultaneously carrying out a resistance-formingprocessing of the pattern region.
 24. The flattening method according toclaim 21, wherein at least one of the first polishing and the secondpolishing is carried out while keeping a contact member, disposed in thevicinity of the processing electrode and/or the feeding electrode, incontact with the surface of the metal film of the workpiece.
 25. Theflattening method according to claim 21, wherein at least one of thefirst polishing and the second polishing is carried out while keepingthe processing electrode at a distance of 0.05 to 50 μm from the surfaceof the metal film of the workpiece.
 26. The flattening method accordingto claim 13, wherein the end point of the first polishing is detected bytime management, detection of a table current, or image recognition. 27.A flattening apparatus comprising: a first polishing section forpolishing a surface of a metal film, formed on a workpiece and having apattern region and a field region, in such a manner that the polishingrate of the metal film in the pattern region is higher than thepolishing rate of the metal film in the field region; and a secondpolishing section for polishing the metal film surface in such a mannerthat the polishing rate of the metal film in the field region is higherthan the polishing rate of the metal film in the pattern region.
 28. Theflattening apparatus according to claim 27, wherein at least one of thefirst polishing section and the second polishing section carries outpolishing by electrolytic processing.
 29. A flattening method forprocessing and flattening a surface of a metal film formed on aworkpiece and having initial surface irregularities, comprising: coatingonly recessed portions of the initial surface irregularities of themetal film with a solid or pasty insulating coating material having aresistivity of not less than 10⁶ Ω·cm; and processing the surface of themetal film by electrolytic processing.
 30. The flattening methodaccording to claim 29 further comprising removing the coating materialwhich has not been processed by the electrolytic processing and remainson the surface of the metal film, and further processing the surface ofthe metal film.
 31. A flattening apparatus comprising: a coatingmaterial processing apparatus for coating only recessed portions ofinitial surface irregularities of a metal film with a solid or pastyinsulating coating material having a resistivity of not less than 10⁶Ω·cm; and an electrolytic processing apparatus for processing thesurface of the metal film by electrolytic processing.